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Transatlantic views on garden plants, native plants, invasive plants, books about plants… Plus comment on wildlife, catalog(ue)s, the smartness and the absurdity of plant names, the transatlantic life, fishing, music and more... From Northamptonshire (zone 8) in England and the much icier Pennsylvania (zone 5) in the USA.

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January 17, 2010

Plants for cold climates

In a fortuitous conjunction of unrelated events, I’ve been thinking about plants for cold gardens at a time when Britain is “enjoying” snow and frost unseen since 1963 when I remember the River Thames froze over west of London not far from where I lived, where it’s about 325ft/100metres wide.

[Answers.com, by the way, says “Although the Thames may have frozen slightly since 1814, with rising global temperatures, the demolition of London Bridge and the embankment of the river, it is unlikely it ever happened to any great degree and certainly not in the 20/21st centuries.” – Shows what they know, I was there. Idiots.]

Anyway, Britain is grinding to a halt after the sort of snow we get in Pennsylvania every winter. (Unfortunately, that snow blower went bang in a cloud of smoke and blows no more...) But let’s be fair, the Brits can’t have flotillas of snow plows waiting 45 years to be us, the taxpayers wouldn’t stand for it. But the temperatures at one Scottish weather station have been down to -6F/-22C and more snow is forecast this week. We have freezing rain here in PA and at this desk is a man wondering what will grow in the very coldest parts of the country.

For recently I’ve been revising one of my books that’s been out of print for a while and been doing some new research on plants that grow in cold gardens. Of course Britain is positively balmy (mostly in zone 8) compared with, say, parts of Canada’s Yukon Territory, Alberta, and Saskatchewan which are in zone 1 where winter temperatures are below -50F/-46° C. The coldest parts of the USA are a little less cold, in zone 2, and include Alaska plus a few mountains in Wyoming and Montana.

So there’s cold – only just below freezing in my home town in Britain this last week – and there’s cold.

It’s interesting to see that different sources don’t necessarily agree but the two standouts for me, plants that would really cheer me up after all those months of snow are lilac and creeping phlox.

Rare Find suggests most, but not all, of their varieties of the familiar common lilac, Syringa vulgaris, are hardy down to zone 2; Ground Effects suggests that four forms of moss phlox (P. douglasii and P. subulata) are also tough enough for zone 2. The big fat American Horticultural Society A-Z Encyclopedia of Garden Plants does not agree. What do you think? Any recommendations for plants to take the most ferocious winters?

Hi from, at the moment, un-snowy Toronto, Canada, which is USDA Zone 5 (and 6, in our own wacky Canadian zoning system).

I can say from experience that there's a big difference between sub-zero temps with and *without* snow cover. In Toronto, we don't have the typical snow cover that similarly zoned suburban gardens in our area might have. Right now, we're going through one of our frequent January thaws. That leaves otherwise zone-hardy plants exposed to drying winter winds and sun – not very good for the constitution.

Yes, snow cover is crucial. I don't think Brits appreciate the value of snow cover - until this year much of the country has been mainly snow free for years. And even now it's gone again in most areas.

What suits the plants best is for a big dose of snow to come first, then for it to get cold, then for it to stay cold, and then for it to warm up and spring to come. It's the cold/warm snow/no snow that so many hate. Even so, they can suffer when the snow and the top few inches of soil thaw in spring and it's still frozen underneath. The crowns of the plants sit in icy water - which they hate.

And Tracey at Foxtail Lilly... If you have any good snowy pix of your garden you wizz one or two over... None on the blog, I see.

Thank you, Graham, for the kind mention. Sometimes I feel a bit of a sham calling myself a cold climate gardener. Partly because it is not as cold here as it used to be, and partly because it never was as cold as it gets in (US)Zones 1, 2 and 3. But I try to keep a list of resources to help all gardeners trying to garden in these challenging conditions: http://www.coldclimategardening.com/cold-climate/

I have to disagree that Britain is mostly zone 8 (US) climate wise! I garden in Scotland and regularly find that most British gardening books list plants that would not be happy here at all. In the West of Scotland it is the amount of winter wet that can be a real problem - using just hardiness in temperature terms is not enough. This year was unusually cold but we had a fall of snow (unusual) that did actually protect the plants from the -10C it went down to here in West Central Scotland. A good book to get started in Scotland would be "Garden plants for Scotland" by K Cox.

You're right in one crucial aspect of all this - it's not just about temperature. The map here http://tinyurl.com/yfc96wq (scroll down) shows most of the British Isles in zone 8, with some mountainous areas in zone 7 and many coasts, the south west and much of Ireland in zone 9. But yes, Andrea, winter wet is a crucial factor - but not one easily measured by a number.

Thanks for the shout-out. I actually use the American Horticulture Society A-Z Encyclopedia of Garden Plants as one of my sources when I'm writing the plant descriptions on our website. The other source I usually use is this website: http://perennials.com/ and that is where I got the information about phlox being hardy to zone 2.